Field of the Invention
The present invention relates to optical fibers, in particular the cleaving of optical fibers to produce a flat end on the fiber.
Description of Related Art
There are many advantages to transmitting light energy via optical fiber waveguides and the use thereof is diverse. Single or multiple fiber waveguides may be used simply for transmitting visible light to a remote location. Complex communication systems may transmit multiple specific optical signals. These devices often require the coupling of fibers in end-to-end relationship with the coupling representing a source of light loss. The cleaved end should be smooth and defect-free. If the ends of the fiber are uneven, excessive light loss can result due to reflection and refraction of light at the cleaved end surface (e.g., a splice or juncture region). For the vast majority of fiber optic applications, it is important to cleave the fiber such that the end of the fiber is completely flat in preparation for coupling. When placing optical fibers in end-to-end relationship, to minimize light loss, it is desirable to have the end faces of the fibers be smooth and lie in a plane perpendicular, or at a specific angle, to the axis of the fibers. In short, the cleaved fiber end face needs to be a single plane that is mirror quality to optimize coupling between fibers in demountable connectors, permanent splices and photonic devices.
In theory, an optical fiber can be cleaved to produce a flat end face by propagating crack growth in controlled fashion. In summary, optical fiber cleaving requires two principle steps: (a) scribing a crack (i.e., a tiny fracture) in the fiber (e.g., at a point on the circumference or around the circumference of the fiber), which serves as an initial shallow crack or fracture at the surface, and (b) applying a suitable tensile stress to cause the scribed crack to grow and propagate across the cross-section of the optical fiber, beginning at the circumference and growing radially towards the center.
Conventional cleaving is done by either use of mechanical cleaving or laser cleaving. Heretofore, according to one conventional mechanical cleaving approach to produce a break at a desired section of the optical fiber, the coating at that section is stripped off. The optical fiber may be first placed under axial tension, and then the bare section of the optical fiber is scribed to initiate a crack. The resulting cleave angle and surface features are a direct result of both the quality of the scribe and axial stress and/or strain distribution in the optical fiber. The axial tension applied is necessary to propagate the crack. However, too much tension will cause the crack to propagate too fast, creating hackle on the cleaved end. If too little tension is used, the scribing edge will be required to penetrate too deeply into the fiber to initiate the crack, giving a poor cleave.
Given the imperfections created at the cleaved ends of the fibers, current cleaving approaches involve conventional cleaving of the optical fiber followed by mechanical or laser polishing of the resultant end face to eliminate imperfections of the cleaved face non-planar form. Such polishing step can be automated, but it requires elaborate and expensive equipment and a rather complex procedure, which limit the operation to being performed in a factory or laboratory.
U.S. Patent Application Publication No. US2012/0000956 A1 (which had been commonly assigned to the assignee of the present invention, and fully incorporated by reference herein) discloses a deterministic cleaving process that can be simply and reliably deployed to properly cleave optical fibers to obtain smooth ends, so as to minimize light loss when the fibers are subsequently coupled. In accordance with the disclosure, axial tension is applied to an optical fiber that had been scribed at the intended cleave location, wherein the axial tension is applied in a time-varying manner to maintain the stress intensity factor for crack on the fiber within an acceptable level to produce a stable crack growth from the circumference towards the center at a reasonable rate to cleave the fiber. Careful control of the applied tension force with time acts to control the velocity of the propagating crack by maintaining a substantially constant stress intensity factor. In one embodiment, the applied axial tension force is reduced with time and/or crack growth. As a result, the strain energy in the fiber material is released by formation of a single plane with an optical quality surface without requiring polishing. A substantially flat optical surface of enhanced optical quality is formed at the cleaved end of the optical fiber.
To facilitate optical fiber cleaving processes, such as the deterministic optical fiber cleaving process disclosed in U.S. Patent Application Publication No. US2012/0000956 A1, there is a need to develop an effective, convenient and reliable mechanism to apply axial tension in a controlled manner.